Abstract
The concentrations of Biochemical oxygen demand (BOD) and ammonium nitrogen in river waters is returning to the early 1960s, but potassium permanganate consumption and total organic carbon (TOC) concentrations does not return. It is thought that their cause comes from the not decreasing of the refractory dissolved organic matter. It seems that refractory dissolved organic matter in raw water is originated from treated water of wastewater treatment plant.
These organic compositions of hydrophobic organic matter and hydrophilic organic matter in refractory dissolved organic matter are not elucidated.
